1. Field of the Invention
This invention relates to improvements in measuring apparatus and method for use in fitting ophthalmic lenses in spectacles frames.
2. Description of the Prior Art
Fitting lenses to spectacles frames requires, in each case of each lens, the taking of measurements which can be used to locate the lens optical center in proper relationship relative to the patient's visual axis when the spectacles are worn.
While various measuring scales and fixtures are used for this purpose (the apparatus of U.S. Pat. No. 4,055,900 being exemplary) less than optimum accuracy of measurement has resulted principally from a lack of means or method of compensating for deviation of visual axis from pupil center.
A patient's visual axes do not necessarily exit from the centers of respective pupils but may do so nasally or temporally to the extent of 0.1 to 0.2 mm for example. Accordingly, the techniques used heretofore of referencing from the center or other arbitrarily selected points on a patient's pupil fail to provide an assurance of whether spectacles frame measurements so taken accurately represent the true distances needed to ultimately properly locate a lens optical center relative to the patient's visual axis.
It is, accordingly, a principal object of this invention to provide novel means and method of assuring accurate alignment of lens optical center relative to a patient's visual axis in the case of each lens of a glazed spectacles frame intended to be worn by the patient.
A further object is to provide means and method for locating the position at which a patient's visual axis intersects the plane of a lens rim of a spectacles frame when the frame is properly fitted to the patient.
Other objects and advantages of the invention will become apparent from the following description.